ACAEINA OR MITES. 105 



tube is padded with, deposits her eggs, in a cocoon of pale silk 

 attached to its end. A portion of this tuhe generally hangs 

 outside the subterranean part, so as to protect it. Trap-door 

 spiders belong here. The second division includes all the other 

 spiders, those with which we are best acqupnted, such as the 

 EpeiridoB, or Orb-weavers, &c. (fig. 40, a). The Drassidce (b) 

 may often be noticed,- — narrow - bodied spiders which live in 

 tubular silken cells, open at each end. These cocoon -like 

 masses we find under the bark of trees, and amongst moss 

 and leaves : from these shelters the spider darts out to hunt 

 its prey. For an account of these and other spiders the reader 

 is referred to Murray's excellent ' Economic Entomology,' which 

 deals with spiders, mites, and other Arachnoidea. 



Acarina or Mites. 



The Mites are of great importance, as many of them are para- 

 sitic, not only upon animals, but upon plants and man. The 

 Acarina are mainly very minute animals, many being no more 

 than -sTirtli of an inch in length; and yet it is these minute 

 forms that cause the most serious pathologic disturbances in 

 animals and the most serious plant diseases. In all mites, and 

 the similarly grouped ticks, the head, thorax, and abdomen are 

 united into one solid body. The internal parasitic forms are 

 generally white or pale-creamy colour. They are provided with 

 a biting and piercing mouth. Amongst the more important dis- 

 eases produced by them are sheep-scab, mange, and itch. They 

 also affect poultry, causing feather-eating, scaly-leg, and in plants 

 various " galled " appearances only too common on some of our 

 fruit-trees. There are also innumerable species that live upon 

 invertebrate animals and in the water. Xhese latter we need 

 not refer to again. Most mites, like spiders, have four pairs of 

 legs when mature, the young having only three pairs. The fused 

 head, thorax, and abdomen soon separate them from the spiders. 

 The so-called red-spider of the hop, Tetranyehm telarius, and the 



